Rather than leather just being dropped by animals. Hide is dropped instead. as you see it has no use individually. but can be tanned into leather. Hide is dropped by Wolves, hounds and cows.(allows mod support)Leather is a highly used material in forging. used for armours, handles, and belts within all sorts of creations

Tanning rack

Allows the hanging of raw hides to be cut or shaved into raw leathers

Knife

(See forging) Made with most metals

Shaving

Shaving is the process of scouring the fur and impurities off skin. This is the first thing you do.

Salt

Right-click in salt water when holding paper to retrieve saltimportant: Water is just water, "Salt water" is determined by a large water source that is bedded by sand, must be at least 3x3 from the centre.
Put salted paper on crafting grid OR cook in furnace/oven

Process

To tan leather. Place hide on the tanning rack. Right-click it with a knife until it finishes, right-click to remove. Take the "Raw Leather" and put salt or flux together with it. And then clean it off by right-clicking water(any water) cauldrons can be used, but need a shift-right click (cauldrons are badly implemented)

Cutting / craft Leather Strips

Or you click the leather on a rack with sheers to cut it into strips(if done directly after shaving leather; it will retrieve more strips: because hide yields more than 1 leather)